Generally, for semiconductor devices such as semiconductor laser devices and high performance MPUs (microprocessing units) used in optical communications or the like, the efficient release of heat generated by the devices is very important for preventing malfunctions. In recent years, advances in semiconductor device technology have resulted in devices with higher power outputs, higher speeds and higher integration, and there have been increasingly strict requirements for heat dissipation. For this reason, a high thermal conductivity is generally required, even for heat dissipation components such as heat sinks, so copper (Cu), which has a high thermal conductivity of 390 W/mK, has been used.
On the other hand, along with higher power outputs, each semiconductor device has become larger in size, and the problem of the mismatch in thermal expansion between the semiconductor device and the heat sink used for heat dissipation has surfaced. In order to address these issues, there has been a demand for the development of heat sink materials that have both a high thermal conductivity and a coefficient of thermal expansion matching with that of semiconductor devices. As such a material, a metal and ceramic composite, for example, an aluminum (Al) and silicon carbide (SiC) composite, has been proposed (Patent Document 1).
However, no matter how conditions are adjusted, the thermal conductivity of an Al—SiC based composite material is at most 300 W/mK, and there has been a demand to develop a heat sink material having a thermal conductivity that is even higher than the thermal conductivity of copper. As such a material, a metal-diamond composite material, in which the high thermal conductivity of diamond and the large coefficient of thermal expansion of metal are combined to achieve high thermal conductivity and coefficient of thermal expansion close to that of semiconductor materials, has been proposed (Patent Document 2).
Additionally, in Patent Document 3, the formation of a β type SiC layer on the surface of diamond grains suppresses the generation of metal carbides having low thermal conductivity formed during compositing and improves the wettability by a molten metal to improve the thermal conductivity of the resulting metal-diamond composite material.
Further, since diamond is a very hard material, the metal-diamond composite material obtained by compositing diamond with a metal is similarly very hard and is a material that is difficult to work. For that reason, most of the metal-diamond composite materials cannot be worked by common diamond tools, and so the problem is how to profile a metal-diamond composite material at a low cost so that the metal-diamond composite material can be used as a heat sink that is small in size and exists in various shapes. With regard to this problem, metal-ceramic composite materials can conduct electricity and so working methods such as electrical discharge cutting have also been investigated.    Patent Document 1: JP-A H9-157773    Patent Document 2: JP-A 2000-303126    Patent Document 3: JP-T 2007-518875